The present invention relates to a switching power supply that delivers electric power from a DC power supply to a DC load via a transformer.
Referring to FIG. 19, a conventional fly-back-type switching power supply includes a bridge rectifier Rec that rectifies an AC input and produces pulsating DC power. The pulsating DC power passes through an input reactor L1 and a series diode D4 to a primary winding N1 of a transformer Tr. A switch Q1 is connected in series with primary winding N1. The series combination including input reactor L1, switch Q1 and primary winding N1 is connected in parallel with bridge rectifier Rec. A capacitor C1, preferably an electrolytic capacitor, is connected in parallel with the series combination of primary winding N1 and switch Q1. A snubber capacitor Cs is connected in parallel with switch Q1. A switch Q3 is connected between the output of input reactor L1 and a common connection of bridge rectifier Rec.
When switch Q1 is ON, energy is stored in primary winding N1. When switch Q1 is OFF, stored energy is released through a secondary winding N2. The output voltage is regulated by controlling the ON and OFF times of switch Q1.
In the circuit of FIG. 19, so-called soft switching (zero voltage switching), causes switch Q1 to switch ON when the voltage across snubber capacitor Cs is at its lowest value. This is accomplished by selecting values of the leakage inductance of primary winding N1 and the capacitance of snubber capacitor Cs so that these elements resonate at the switching speed. Soft switching reduces power loss and improves noise suppression.
Switch Q3 is switched ON to produce input current flow through input reactor L1. The input current flow improves the power-factor of the circuit. When switch Q3 is switched ON, energy stored in the input reactor L1 is fed to electrolytic-type capacitor C1. Switching switch Q3 ON and OFF improves the power-factor even when the input voltage is low, since input current flows whenever the switching power supply is operating.
The OFF-period of switch Q1 is set to a length of time determined by the resonant frequency of the series combination of the leakage inductance of primary winding N1 and snubber capacitor Cs. The OFF-period of switch Q1 must be related to the resonant frequency to produce soft switching in the switching power supply of FIG. 19. In contrast, the output voltage is regulated only by the ON-period of switch Q1. Since the ON-period and the OFF-period of switch Q1 are governed by different criteria, the switching frequency of switch Q1 must therefore vary to regulate the output voltage while maintaining soft switching.
Switching power supplies used in television sets and display devices have switching frequencies that are generally synchronized with the deflection frequency. Therefore, a conventional switching power supply that depends on its switching frequency to regulate output voltage is not useful in such variable frequency applications.
The use of two separate switches Q1, Q3 for voltage regulation and power-factor improvement respectively, increases the noise level of the resulting output of the switching power supply. In addition, diode D4 in series with switch Q1 causes a voltage drop when current flows and decreases the switching power supply efficiency.
In view of the foregoing, it is an object of the present invention to provide a switching power supply which overcomes the above-described drawbacks ofthe prior art.
It is a further object of the present invention to provide a switching power supply that facilitates soft switching at arbitrary frequencies.
It is another object of the present invention to provide a switching power supply with an improved power factor using a simplified scheme.
It is still another object of the present invention to provide a switching power supply that takes advantage of soft switching.
It is yet another object of the present invention to provide a switching power supply that facilitates switching at arbitrary frequencies, takes advantage of soft switching and obtains an improved power factor using a simplified scheme.
It is a still further object of the present invention to provide a switching power supply that has an improved efficiency when driving loads substantially lighter than a rated load.
It is a yet further object of the present invention to provide a switching power supply with switches and control circuits that are integrated into a single integrated circuit.
Briefly stated, the present invention provides a switching power supply that uses zero-current and zero-voltage switching to reduce switching noise. A main switch and an auxiliary switch channel current and voltage between various component paths to maintain a DC output voltage while switching in zero-current or zero-voltage states. Switch ON-OFF time ratios are controlled with a simple scheme to improve the circuit power factor. The switching rate is set to arbitrary frequencies, with switch ON time and OFF time being controlled independently. Conventional losses in efficiency when driving a load substantially less than the rated load are avoided. The switches and control functions can be implemented on an integrated circuit, reducing size and improving efficiency. Thus a flexible, simple design improves efficiency while reducing noise and manufacturing costs.
According to a first aspect of the invention, there is provided a switching power supply that includes a DC power supply; a transformer connected to the DC power supply, the transformer including a primary winding and a secondary winding; a rectifying and smoothing circuit connected to the secondary winding of the transformer; an input reactor; a main semiconductor switch connected in series to the primary winding; a first diode connected in opposite parallel to the main semiconductor switch; a snubber capacitor connected in parallel with the main semiconductor switch; a series circuit for discharging the electric charge of the snubber capacitor, the series circuit including a resonance reactor and an auxiliary semiconductor switch; a second diode connected in opposite parallel to the auxiliary semiconductor switch; and a capacitor connected in parallel to the primary winding.
Advantageously, the series circuit further includes a resonance capacitor. Advantageously, the switching power supply further including a tertiary winding interposed between the primary winding of the transformer and the main semiconductor switch; and a third diode connected between the auxiliary semiconductor switch and the connection point of the primary winding and the tertiary winding, the third diode connecting the capacitor in parallel to the primary winding.
Advantageously, the switching power supply including a reactor interposed between the primary winding of the transformer and the main semiconductor switch; and a third diode connected between the auxiliary semiconductor switch and the connection point of the primary winding and the reactor, the third diode connecting the capacitor in parallel to the primary winding.
According to a second aspect of the invention, there is provided a switching power supply that includes a DC power supply; a transformer connected to the DC power supply, the transformer including a primary winding and a secondary winding; a rectifying and smoothing circuit connected to the secondary winding of the transformer; an input reactor; a main semiconductor switch connected in series to the primary winding; a first diode connected in opposite parallel to the main semiconductor switch; a snubber capacitor connected in parallel to the main semiconductor switch; a series circuit for discharging the electric charges of the snubber capacitor, the series circuit including a resonance capacitor, a resonance reactor and an auxiliary semiconductor switch; and a second diode connected in opposite parallel to the auxiliary semiconductor switch.
Advantageously, the transformer further includes a quaternary winding substituting for the input reactor.
According to a third aspect of the invention, there is provided a switching power supply that includes a DC power supply; a transformer connected to the DC power supply, the transformer including a primary winding and a secondary winding; a rectifying and smoothing circuit connected to the secondary winding of the transformer; an input reactor; a main semiconductor switch connected in series to the primary winding; a first diode connected in opposite parallel to the main semiconductor switch; a series circuit including a capacitor and an auxiliary semiconductor switch, the series circuit connected in parallel to the primary winding and the main semiconductor switch; a second diode connected in opposite parallel to the auxiliary semiconductor switch; and a third diode connected between the auxiliary semiconductor switch and the connection point of the primary winding and the main semiconductor switch.
Advantageously, the transformer further includes a tertiary winding substituting for the input reactor.
Advantageously, the transformer further includes a tertiary winding interposed between the capacitor and the auxiliary switch of the series circuit, the tertiary winding substituting for the input reactor.
According to a fourth aspect of the invention, there is provided a switching power supply that includes a rectifier for converting an AC voltage to a DC voltage; a transformer, the transformer including a primary winding, a secondary winding and a tertiary winding; a semiconductor switch connected in series to the primary winding; the semiconductor switch and the primary winding constituting a first series circuit; the rectifier being connected in parallel to the first series circuit; an electrolytic capacitor connected in parallel to the first series circuit; a smoothing and rectifying circuit connected to the secondary winding to deliver DC electric power to a load by the switching-on and -off of the semiconductor switch; and a reverse-recovery diode connected in series to the tertiary winding; the reverse-recovery diode and the tertiary winding constituting a second series circuit connected to the connection point of the rectifier and the electrolytic capacitor.
By the configuration described above, a voltage is generated across the tertiary winding in opposite polarity to the reverse-recovery diode when the semiconductor switch is switched on. The voltage makes the reverse-recovery diode recover reversely. The reverse-recovery diode then interrupts the current. Since the conventional low-speed diodes are satisfactorily employable in the rectifier, the manufacturing costs of the switching power supply are reduced.
According to a fifth aspect of the invention, there is provided a switching power supply that includes a rectifier for converting an AC voltage to a DC voltage; a transformer including a primary winding, a secondary winding, a tertiary winding and a quaternary winding; a first semiconductor switch connected in series to the primary winding; the first semiconductor switch and the primary winding constituting a first series circuit; the rectifier being connected in parallel to the first series circuit; an electrolytic capacitor connected in parallel to the first series circuit; a smoothing and rectifying circuit connected to the secondary winding to deliver DC electric power to a load by the switching-on and -off of the first semiconductor switch; a diode connected in series to the quaternary winding; the diode and the quaternary winding constituting a second series circuit connected in series to the electrolytic capacitor; a second semiconductor switch connected in series to the tertiary winding; the second semiconductor switch and the tertiary winding constituting a third series circuit connected in parallel to the electrolytic capacitor.
Since the quaternary winding discharges through the diode, the electrolytic capacitor, the rectifier and the AC power supply, an input current flows even when the input voltage is lower than the voltage of the electrolytic capacitor. As a result, the conduction angle is widened and, therefore, the power factor is improved. Since the input voltage and the voltage generated across the quaternary winding are applied to the electrolytic capacitor, the electrolytic capacitor is charged up by the voltage higher than the peak value of the input voltage.
Current flows in the circuit even when the sum of the voltage of the AC power supply and the voltage across the quaternary winding is less than the voltage across the electrolytic capacitor. Although the electrolytic capacitor is not charged, a current flows through the series circuit consisting of the primary winding and the first semiconductor switch, since the series circuit is connected directly to the rectifier. As a result, the conduction angle is widened.
According to a sixth aspect of the invention, there is provided a switching power supply that includes a DC power supply; a transformer including a primary winding; a main semiconductor switch; the primary winding and the main semiconductor switch constituting a first series circuit connected in series to the DC power supply; a second series circuit including a resonance capacitor, resonance reactor and an auxiliary semiconductor switch, the second series circuit being connected in parallel to the main semiconductor switch to switch on and off only the auxiliary semiconductor switch when the output electric power of the switching power supply is low including in the waiting mode of operation.
Advantageously, the transformer further includes a tertiary winding substituting for the resonance inductance.
According to a seventh aspect of the invention, there is provided a switching power supply that includes a main power supply for supplying electric power for driving a load- the main power supply including a DC power supply, a first transformer including a first primary winding, a first semiconductor switch, the first primary winding and the first semiconductor switch constituting a first series circuit connected in series to the DC power supply, and a first integrated circuit, connected to the first semiconductor switch, for driving and for controlling the first semiconductor switch; and a sub power supply for supplying electric power in the waiting mode of operation; the sub power supply including the DC power supply, a second transformer including a second primary winding, a second semiconductor switch, the second primary winding and the second semiconductor switch constituting a second series circuit connected in series to the DC power supply, and a second integrated circuit, connected to the second semiconductor switch, for driving and for controlling the second semiconductor switch; the first semiconductor switch, the first integrated circuit, the second semiconductor switch and the second integrated circuit being integrated and mounted on a common package.
Advantageously, either one or both of the main power supply and the sub power supply include either one of the switching power supply devices described above.
Advantageously, the integrated circuits for driving and for controlling the first and second semiconductor switches are integrated into a common control IC.
According to an embodiment of the present invention there is provided a switching power supply adapted for use with an input DC power supply comprising: an input reactor, a transformer having at least a primary winding and a secondary winding, the primary winding of the transformer connected to the DC power supply through the input reactor, a rectifying and smoothing circuit connected to the secondary winding of the transformer, a main semiconductor switch connected in series with the primary winding, a first diode connected in opposite parallel with the main semiconductor switch, a snubber capacitor connected in parallel with the main semiconductor switch, a series circuit including a resonance component and an auxiliary semiconductor switch connected in parallel with the main semiconductor switch, the series circuit being effective to discharge an electric charge of the snubber capacitor, and a second diode connected in opposite parallel with the auxiliary semiconductor switch.
According to another embodiment of the present invention there is provided a switching power supply adapted for use with an input DC power supply comprising: an input reactor, a transformer having at least a primary winding and a secondary winding, the primary winding of the transformer connected to the DC power supply through the input reactor, a rectifying and smoothing circuit connected to the secondary winding of the transformer, a main semiconductor switch connected in series with the primary winding, a first diode connected in opposite parallel with the main semiconductor switch, a series circuit including a capacitor and an auxiliary semiconductor switch, the series circuit connected in parallel with the primary winding and the main semiconductor switch, a second diode connected in opposite parallel with the auxiliary semiconductor switch, and a third diode interposed between the primary winding and the auxiliary semiconductor switch.
According to still another embodiment of the present invention there is provided a switching power supply comprising: a rectifier effective to convert an AC voltage to a DC voltage, a transformer having at least a primary winding, a secondary winding and a tertiary winding, a semiconductor switch connected in series with the primary winding, the primary winding connected to the rectifier through the tertiary winding, an electrolytic capacitor connected in parallel with the semiconductor switch and the primary winding, a smoothing and rectifying circuit connected to the secondary winding, the smoothing and rectifying circuit being effective to deliver DC electric power to a load, the semiconductor switch being effective to regulate the DC electric power when the semiconductor switch is switched ON and OFF, and a high-speed reverse-recovery diode interposed between the tertiary winding and a connection point of the electrolytic capacitor and the primary winding.
According to still another embodiment of the present invention there is provided a switching power supply comprising: a rectifier effective to convert an AC voltage to a DC voltage, a transformer having at least a primary winding, a secondary winding, a tertiary winding and a quaternary winding, a first semiconductor switch connected in series with the primary winding, the rectifier being connected in parallel with the first semiconductor switch and the primary winding, a smoothing and rectifying circuit connected to the secondary winding, the smoothing and rectifying circuit being effective to deliver DC electric power to a load, the semiconductor switch being effective to regulate the DC electric power when the semiconductor switch is switched ON and OFF, a first series circuit including the quaternary winding, a diode and an electrolytic capacitor, the first series circuit connected in parallel with the first semiconductor switch and the primary winding, a second semiconductor switch connected in series with the tertiary winding, and the second semiconductor switch and the tertiary winding connected in parallel with the electrolytic capacitor.
According to yet another embodiment of the present invention there is provided a switching power supply adapted for use with an input DC power supply comprising: a transformer having at least a primary winding and a secondary winding, a main semiconductor switch connected in series with the primary winding, the primary winding connected to the DC power supply, a smoothing and rectifying circuit connected to the secondary winding, the smoothing and rectifying circuit being effective to deliver DC electric power to a load, a series circuit including a resonance capacitor, a resonance reactor and an auxiliary semiconductor switch, the series circuit connected in parallel with the main semiconductor switch, the main semiconductor switch being switched OFF when the switching power supply drives a light load substantially smaller than a rated load, and the auxiliary semiconductor switch being effective to regulate the light load when the auxiliary semiconductor switch is switched ON and OFF.
According to another embodiment of the present invention there is provided a switching power supply adapted for use with an input DC power supply comprising: a main power supply effective to supply electric power to a rated load, the main power supply including a first transformer, the first transformer having at least a first primary winding, the at least first primary winding connected to the DC power supply, a first semiconductor switch connected to the at least first primary winding, a first integrated circuit connected to the first semiconductor switch effective to drive and control the first semiconductor switch, a sub power supply effective to supply electric power to a load substantially smaller than the rated load, the sub power supply including a second transformer, the second transformer having at least a second primary winding, the at least second primary winding connected to the DC power supply, a second semiconductor switch connected in series with the at least second primary winding and a second integrated circuit connected to the second semiconductor switch effective to drive and control the second semiconductor switch.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.